Pulse or digital communications – Pulse position – frequency – or spacing modulation
Reexamination Certificate
2000-11-27
2004-07-27
Vo, Don N. (Department: 2631)
Pulse or digital communications
Pulse position, frequency, or spacing modulation
C375S355000
Reexamination Certificate
active
06768773
ABSTRACT:
The invention relates to an arrangement for determining the phase position of a data signal in the form of digital sampling values, comprising asynchronous modulated data having a known modulation frequency.
A data signal whose bits or data are modulated asynchronously but whose modulation frequency is known may have different phase positions which are to be determined. The data signal is present in the form of digital sampling values. Particularly when the sampling frequency at which the digital sampling values are gained is not coupled to the modulation frequency of the data, it is not known which sampling value represents which bit and where this sampling value is located within this bit. Considerable problems then occur when decoding the bits, or the decoding may be liable to disturbances, for example, noise.
To solve this problem, a signal-separating device is known from EP-A-0 472 756 which is used for separating a teletext signal from a video signal. The circuit operates in a very elaborate way and includes an integrating device which supplies a half-position signal characterizing the signal means of the individual bits of the data signal, and a residual value signal. A residual value signal evaluation device evaluates each residual value and determines, by means of a selection control signal, how the value of the current signal bit is to be evaluated. To this end, a selection device is available which forms the respective leading mean value or the trailing mean value from each current sampling value and each previous or subsequent sampling value and, by means of the selection control signal, selects the value suitable for the evaluation. A further phase correction device evaluates a signal sample supplied by a slope logic device, indicating whether the current sampling value approximates a slope of a signal. The same device then controls a change of the integration period when the residual value signal is within a predetermined residual value signal range. This arrangement operates in a very elaborate manner and can only perform a kind of estimation of the position of the individual bits.
It is an object of the invention to provide an arrangement of the type described in the opening paragraph, which is capable of determining the phase position of the individual bits, solves the above-mentioned problems, has a possibly simple construction and may at least partly be realized also in software.
According to the invention, this object is solved in that the arrangement comprises means performing a first and/or a second method of determining the bit positions of the sampled data signal, in that in the first method at least a set of three or five consecutive sampling values is searched whose mean sampling value is larger than or smaller than the neighboring outer sampling values of the set and in which the difference(s) of those outer sampling values being equidistantly spaced apart from the central sampling value fall below a predetermined threshold value, while upon detection of such a data set the position of the central sampling value and an associated position number indicating the position of the bits in the data signal are stored in a memory, in that in the second method a set of four consecutive sampling values is searched whose two central sampling values are approximately equally large and whose central value is smaller or larger than the central value of the two outer sampling values and in which the difference of the outer sampling values falls below a predetermined threshold value, while upon detection of such a data set the bit position in the center between the two central sampling values and an associated position number are stored in a memory (
10
), and in that the arrangement determines a phase signal from at least two determined bit positions, the position numbers assigned thereto and the period length of the bits of the data signal, which phase signal supplies the phase position of the bits of the sampled data signal relative to a predeterminable starting point.
In the invention, the phase position of the individual bits of the asynchronous modulated data are determined, while a subsequent decoder, which does not form part of the invention and which determines the data, receives a phase signal indicating, to the decoder, the phase position of the asynchronous modulated data in the data signal.
This problem may even be greater in that in the case of an unfixed coupling of the sampling frequency at which the digital sampling values of the data signal are generated and the modulation frequency at which the data in the data signal are modulated the phase position is not fixed or is not known. Then there is a drift between the individual sampling values and the position of the bits in the data signal. It is thus not known which sampling value represents which data bit or where this sampling value is located within the signal variation of this bit.
It is exactly this problem that the invention should solve and supply a phase signal indicating to a subsequent decoder the phase position of the modulated bits of the data signal relative to a predeterminable starting point.
To be able to supply such a phase signal, the arrangement according to the invention must be capable of determining the exact position of the bits in the data signal. For this purpose, the arrangement comprises means which perform a first and/or a second method in which the bit positions of the sampled data signals are determined. In this method, given bit positions having a marked position relative to the sampling values are selected, for example, within a predeterminable time interval or data interval of the data signal, so that the position of the bits can be concluded relatively precisely from the sampling values.
In the first method, these means select a set of three or five consecutive sampling values, for which the following conditions apply. The central sampling value of these three or five or more sampling values must be larger or smaller than all of its neighboring outer sampling values, i.e. than the other two or four sampling values of this set of sampling values. Furthermore, the difference between the outer sampling values, each being equidistantly spaced apart from the central sampling value, must be minimal. Thus, when three sampling values in one set are used in this method, the difference between these two values must be minimal. When five sampling values in one set are used for performing this method, the difference between the first and the last sampling value of this set of sampling values must be minimal and, furthermore, the difference between the second and the fourth sampling value of this set must also be minimal.
When a set of consecutive sampling values is found, for which these conditions have been fulfilled, it can be assumed that the central sampling value of this set of sampling values quite exactly represents a maximum or a minimum in the signal variation of the data signal. This sampling value thereby fairly exactly represents a central position of a bit in the data signal. Since exactly this bit is searched, the position of the central sampling value is stored in a memory when detecting such a data set for which the conditions described above have been fulfilled. Furthermore, the position of this bit in the data signal is stored, i.e., for example, which bit as from a predeterminable starting point is concerned. Also this value is stored as a position number in the memory.
After performing the first method, for example, for a given period of time or a given section of the data signal, a plurality of bit positions is found for which the conditions described above have been fulfilled and whose position numbers are then stored in the memory.
Additionally or alternatively to the first method, the means perform a second method in which a set of four consecutive sampling values is searched, in which the difference between the two central sampling values falls below a predetermined threshold value and in which these two sampling values are both smaller or both larger
Ghulamali Qutbuddin
Koninklijke Philips Electronics , N.V.
Ure Michael J.
Vo Don N.
LandOfFree
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